Impact of moderate vs stringent TSH suppression on survival in advanced differentiated thyroid carcinoma

To assess (i) the influence of Thyrotropin (TSH) suppression at a level of <0·1 mU/l and (ii) whether FT3 and FT4 levels have a prognostic significance independently of TSH values with regard to survival in patients with differentiated thyroid carcinoma (DTC) and distant metastases.

In a retrospective patient chart study, we reviewed survival in 157 DTC patients with distant metastases treated between September 1985 and 1 July 2010. Patients with at least three available FT3 and FT4 values during TSH suppression were eligible.

Fifty-three of 157 patients died from DTC. DTC-specific survival was significantly better in patients with a median TSH level ≤0·1 mU/l (median survival 15·8 years) than those with a non-suppressed TSH level (median survival 7·1 years; P < 0·001). However, there was no further improvement in survival caused by TSH suppression to a level ≤ 0·03 mU/l (P = 0·24). FT3 and FT4 levels were also significantly associated with poorer survival; of these, only the prognostic value of FT3 was independent from that of TSH levels.

The care of patients with DTC and distant metastases is like walking an endocrinological tightrope: non-suppressed TSH levels, that is, >0·1 mU/l, are associated with an impaired prognosis. There is, however, no prognostic benefit from suppressing TSH to levels lower than 0·1 mU/l. On the contrary, an improvement in prognosis might be achieved by keeping FT3 levels as low as possible.